Hi all,
I was just discussing things here with Sebastian, as he was just sitting next
to me.
Now I'm writing down what we were talking about.
There were multiple things we both not that happy with and here's our proposal:
1) Rename Address to Query (Naming could be discussed)
2) Adding Type and Array Size (Optional) to the query string ($DB1.$W54:UINT[4])
3) Define 2 types of ItemRequest/-Responses:
1) Containing generic type information: Able to do sanity-checks when
parsing, response item contains only a generic get() or get(itemNumber) methods
2) Without generic type information: No sanity check. Saves data in a
generic way (maybe byte-array) and provides type-accessors: getInteger(),
getDouble(), getFloat(),...
4) Splitting up response items in single item responses and multi item responses
Now to the reasoning:
1) At the beginning we only had Addresses. But now we are extending the simple
Addresses with information on how to interpret the address. This no longer
feels like a pure "address".
2) Well adding the explicit type to any former address (I would suggest to do
it the same way for every driver) ... I think we discussed the need for this.
The next thing was that when using the API the size/length field and how we
access these values sort of felt uncomfortable. Therefore I would like to use
the opportunity to add the size to the query string ... in above example the
UINT[4] would mean that 4 UNIT values should be read (and not 4 bytes).
3) The two types of request (and matching response items) would simply help the
two types of users: I for my part more construct large multi-item ReadRequests
where handling all the generic types does make things more complicated for me.
I prefer to have items and to access them with typed accessors. On the other
side when accessing simpler or single-item requests, there is a great benefit
for code simplicity.
4) When using the response items it always felt strange to have these
convenience single-item-accessors which throw exceptions if the response is
multi-item.
Now to your suggestions:
I think we are both on the same page conceptually ... think all I am proposing,
is to add the array access to the string and to rename the entire concept.
Especially I think we both agree on storing the information in the
response-item in byte-form and to cast that to the desired type when needed.
Regarding the wrapper pattern ... I don't know if I understood this. But to me
it looks as if we would have to do type-checks depending on the parameter type
... so we have to explicitly write a conditional branch for every supported
type and throw an exception for not-supported ones. So if I use:
responseItem.unwrap(Hurz.class)
This would probably not work ... or did I just get the concept wrong?
I did have a look at your changes and have some observations:
1) Your fork could need updating ;-)
2) Your version of TypedAddress is very focused on S7 as for example an ADS
address could be a simple string (Symbolic addressing), for EtherNet/IP there
is no such byte-offset and bit-offset, there's just
ClassId+InstanceId[:AttributeId] ... also doesn't it support reading of arrays
... I think we should leave the Address in it's simple state as a simple
place-holder.
3) S7BitsWith ... well S7 uses the name of a Data-Transport-Size ... but I
think in our case the X,B,W,D and L are syntactic sugar that should be used
while parsing a query- or address string. We shouldn't even need it afterwards.
4) The S7Type is generally ok the way it is however, should we add all the
types and add which S7 types support them. For example an LINT will only work
on S7 1500 and 1200. If you update your Fork, you should be able to see the
S7ControllerType and S7DataType classes, that I added some time ago. It's sort
of an aggregate of your S7Type and S7BitsWidth (I think) ... please have a look
at that and tell me what you think.
And regarding your question ... you can start discussion threads whenever you
want ... usually you don't have to flag it that way, but it certainly doesn't
hurt. In other projects we usually have a "[DISCUSS]" thread alongside a
"[VOTE]" thread, so the actual voting isn't mixed with discussions about what's
being voted on. I tried to start topics that touch a certain area with a
[]-prefix to trigger people for example with EtherNet/IP knowledge. So as I
said ... there's no formal process on Discussion threads ... only [VOTE]
threads should be reserved to actual things voted on.
Chris
Am 22.08.18, 16:19 schrieb "Julian Feinauer" <j.feina...@pragmaticminds.de>:
Hey all,
we had several discussions about type handling [1,2] in general and in
drivers and especially the addition of type information for the S7 Driver [3].
I am currently implementing the “typed” addresses for the S7 Driver [3] and
wanted to propose the approach there as it could form the basis of the general
“internal” typesystem for all drivers.
Motivation:
Provide all drivers with a common type system to reduce the amount of
driver specific code for “type” handling.
The approach is the following:
I added an abstract class TypedAddress which implements the marker
Interface Address (which is returned from the Driver).
TypedAddress contains all necessary “generic” information to be able to
decode values from a byte[] array, i.e., the offset for byte / bit, the number
of bits used by the value and a Category.
Category encapsulates the “logical type”, i.e., if the value is INTEGER or
DECIMAL, SIGNED or UNSIGNED, STRING, DATE or whatsoever.
For the S7 driver the TypedAddress is extended by the TypedS7Address which
adds S7 Specific properties like memory area.
In case of the S7 flow all subsequent usages of Address in the lower layers
(XXXProtocol) are made with regards to the TypedS7Address.
Furthermore, I suggest to use the Wrapper pattern for the address
interface, see e.g. [5] from java.sql as it makes these instance-checks in the
driver code “nicer”.
What do you think of these changes, do you agree with the approach I use?
@Sebastian
I had a look through the Ads Implementation and I think this approach would
be feasible for the ads implementation too. Is this correct?
@Chris
I’m lacking the feeling of when to start a [DISCUSSION] or how the general
guidelines are here and especially in this project so I’m thankful for advice
Best
Julian
[1]
http://mail-archives.apache.org/mod_mbox/plc4x-dev/201807.mbox/%3C1B180308-0BFA-4203-869C-ABE64D77B203%40c-ware.de%3E
[2]
http://mail-archives.apache.org/mod_mbox/plc4x-dev/201807.mbox/%3CF8E442F3-906C-47D6-9F08-A393F6D11557%40pragmaticminds.de%3<http://mail-archives.apache.org/mod_mbox/plc4x-dev/201807.mbox/%3CF8E442F3-906C-47D6-9F08-A393F6D11557%40pragmaticminds.de%253>E
[3]
http://mail-archives.apache.org/mod_mbox/plc4x-dev/201808.mbox/%3C481F0FC1-0A9B-44F8-B594-C8E825EB5026%40c-ware.de%3E
[4]
https://github.com/JulianFeinauer/incubator-plc4x/tree/add-typed-addresses-s7
[5] https://docs.oracle.com/javase/7/docs/api/java/sql/Wrapper.html
